1. Field of the Invention
The present invention relates to a device making it possible to check or control the clearances of a high pressure compressor casing of a gas turbine. This device can be used for numerous types of gas turbine for aircraft engines.
2. Discussion of the Background
The high heating levels to which a gas turbine is exposed during the flight of an aircraft lead to thermal expansion, which should be controlled in order to improve the performance characteristics of the gas turbine. More particularly, it is important to control the radial clearances between the rotor and the stator, i.e. limit said clearances during the accelerating and cruising phases (essential phases during flying), while avoiding mechanical interference between the fixed part (i.e., stator) and the rotary part (i.e., rotor) of the compressor during a transient phase of the deceleration type with reacceleration.
Several documents propose devices for controlling such clearances and are usually in the form of compressor stators having a double envelope casing, namely an inner envelope supporting the stator blades and an outer envelope, said two envelopes being joined by flexible connections.
French patent application 2,607,198, filed on Nov. 26, 1986 by the present Applicant, proposes a compressor casing comprising an inner envelope having circumferential corrugations, whereof the valleys are located level with the medium of a blade stage and the crests are located at the blade edges. Rows of flexible pillars connect and join the inner and outer envelopes.
FR-2,640,687 proposes installing a plurality of deformable cylindrical bellows within which a variable pressure is maintained by an air sampling duct at the downstream end of the compressor.
The two aforementioned devices make it possible to limit the risks of mechanical interference between the stator and the rotor, but their use is difficult.
French patent application 2,653,171 describes a gas turbine compressor casing constituted by two inner and outer envelopes forming an enclosure and supplied with hot air by a downstream opening. The two envelopes are connected by hollow connecting arms and are linked with an air ventilating circuit or system permitting the circulation of cooling air within the arms. This device requires a cooling circuit for the casing in the essential flight stages of cruising and acceleration and this is expensive from the delivery standpoint.